The present invention relates to high alumina refractory shapes that are used primarily in contact with molten aluminum and which have high resistance to aluminum penetration and buildup of dross.
Refractory shapes, such as brick, are commonly utilized in furnaces and other metallurgical vessels in which molten aluminum is being handled or processed. One of the major problems with such refractory shapes, is a vulnerability to penetration therethrough of the aluminum and reaction therewith as well as dross buildup on the brick. Such penetration and buildup combine to shorten service life for the refractories employed as well as to increase the need for mechanical cleaning of the refractory particularly to remove the dross buildup. Further, because of the buildup a reduced capacity of the metallurgical vessel can result.
Efforts to overcome these problems and to increase the service life of the refractories have not been entirely successful due either to the fact that there is still undesirable aluminum penetration or adhesion to the brick and in some instances the additives used to improve penetration resistance result in undesirable lowering of the hot strength of the shape or brick or adversely affect the processing characteristics making it difficult to make satisfactory shapes.
A generally satisfactory product is that set forth in U.S. Pat. No. 5,190,899 in which a boron phosphate is utilized to increase the penetration resistance without any loss of hot strength or negative effects during processing to form the shape. Such product is a large improvement over the utilization of other materials such as the use of zinc borosilicate frit as set forth in U.S. Pat. No. 4,088,502 or the use of barium sulfate in the case of U.S. Pat. No. 4,126,474. As noted in U.S. Pat. No. 5,190,899 the addition of zinc borosilicate frit presents problems of severe sticking to the press used to form the brick and the use of barium sulfate lowers hot strengths.
With respect to the shapes set forth in U.S. Pat. No. 5,190,899, there remains an undesired degree of penetration and dross buildup during service.